It is well-known that integrated circuits (IC) are often damaged by voltage transients which overload one or more individual devices contained within the IC, resulting in melting, short circuiting or otherwise destroying the device. In the past, various devices and circuits have been employed to protect the IC's and to thereby prevent its destruction by such transients. These protection devices have taken the form of either diodes or transistor circuits that have been included on the chip for internal transient protection. While such devices provide some measure of protection for the IC in which they are included, it has been found that they occupy large areas which might otherwise be used for circuitry and thus enhance the packing density.
One example of a transient is a high voltage spike that may occur in a television receiver which contains low voltage IC's for, for example, video and audio processing. Typically, the anode of a picture tube is biased to about 25,000 volts and if the high voltage anode is rapidly discharged, a high voltage transient will appear at the power supply. Arcing in the picture tube may also unpredictably occur between the anode and one or more of the low potential electrodes. In either event, the high voltage transient which may have either a positive going or a negative going peak in excess of 100 volts, is applied to the IC terminal through the common power supply or by electrostatic pickup on the connecting conductors of a printed wiring board.
Stil another cause of high voltage transients in a television receiver is electrostatic discharge. A build-up of electrostatic charge is usually discharged by the user through the television receiver controls to produce a high voltage transient which may damage IC's in the television receiver.
While there are many high voltage transient protection devices available to the design engineer, he is faced with the problem of having to use valuable chip space for forming the bulky protection devices. On devices containing a large number of pins, it has been found that the protection devices occupy a significant space and, therefore, the chip becomes unduly large and is thus undesirable.